You follow a strict training regimen and a nutrition plan measuring down to the milligram of magnesium you take. But if you can’t digest what you consume properly, it’s going to affect your athletic performance.
You aren’t alone because 13.9% to 61% male athletes and 20% to 80% female athletes experience GI symptoms like bloating, stomach upset, etc, according to a 2026 review. The reasons may vary from exercise intensity, duration, dietary intake, and individual tolerance.
In this blog, we give you practical tips that you can easily implement to understand your gut better and adjust your sports nutrition strategy accordingly.
Why Does Sports Nutrition Upset My Stomach?
Sports nutrition may cause stomach upset due to intense exercise, concentrated sports nutrition, dehydration, baseline gut health, and timing of consuming the diet.
Endurance exercise: According to a 2025 mini-review in the Frontiers in Physiology journal, high-intensity endurance exercises encourage more blood to flow into the skeletal muscle. Naturally, it reduces blood flow in the gastrointestinal tract or digestive tract. Over time, this ongoing restriction may cause microdamages to the GI and gut microbiome. Heat stress, dehydration, and physical rhythmic jolting of running activity can further contribute to this gut distress.
Sports nutrition:Many athletes follow an extreme diet that fails to support real-time digestion. Overconsuming or underconsuming nutrients affects the gut flora and leads to digestive troubles. While fiber is great on rest days, try to limit your intake to less than 2 to 3 grams in your pre-workout meal. Swap your usual oatmeal or whole-grain toast for simple, low-fiber options like a plain white bagel with a little honey or a banana. Sports health drinks may contain dairy or fructose, which may cause stomach upset in some athletes. Hypertonic drinks may contain carbohydrates. They can cause digestive discomfort when you drink them during exercise.
Dehydration:Dehydration is a recurring problem for athletes and this can also contribute to digestive issues. If you start your hard training or race poorly hydrated, your stomach may not move the food properly and this causes indigestion.
Gut health: Personalized nutrition supports gut health for athletes. You need a diet that you can tolerate and this can vary from one person to another. Some people may have trouble digesting high-fiber food or high-protein drinks. Knowing what works for you and what doesn’t, well ahead of competition, can help you understand your baseline gut health to strategize a nutrition plan.
Food timing: Any type of nutrition, such as carbohydrates, fiber, proteins, etc., when taken in sudden large quantities, can disrupt digestion. Consuming high-fiber foods before exercise may slower digestion. Simple carbohydrates before exercise provide necessary nutrition without overstraining the gut. Some athletes may not follow the diet plan properly when they aren’t training, and this can also impact gut health.
How Digestive Problems Affect Athletic Performance?
When your gut isn’t absorbing the carbohydrates you eat, you may feel uncomfortable. More than that, your muscles quickly run out of fuel without energy. You may hit the wall faster, meaning your pacing may drop, your perceived effort may go up, and even a moderate pace may feel challenging. Poor digestion can cause:
Fatigue due to poor energy delivery because your body can’t absorb carbohydrates
Dehydration because fluid isn’t absorbed properly and heavy sweating leads to fluid loss
Inflammation due to physical stress on the body and gut
Race disruption due to digestive symptoms like diarrhea, reflux, vomiting, etc
How to Adjust Sports Nutrition for Digestive Tolerance?
Just like the way you train your muscles, you can train your gut. When you consume carbohydrates during a big race, start eating the same food and drinks during weekly training sessions. This helps you build digestive tolerance and lower race-day bloating.
Personalize your nutrition: The diet that works for you should be uniquely designed for you. Even two athletes of the same age in the same sport will have completely different baseline health and digestive tolerance. Consult with a dietary expert to first understand what your body needs and how you can support energy delivery through food. Then, you may choose sports nutrition supplements to support your dietary goals.
Focus on micronutrients: Micronutrients support gut health. Vitamins B, C, D, and E support bacterial gut diversity. Minerals like zinc, calcium, and magnesium also support microbial balance. At the same time, excess intake of certain nutrients like iron or phosphorus may disrupt gut flora. Personalized intake of micronutrients is necessary, and for added support, you can choose from one of the multivitamin supplements designed for athletes.
Include probiotics: Probiotics feed beneficial gut bacteria and may support the gut microbiome. Probiotic supplements provide different strains of bacteria that may support the digestion of your nutritional plan. Aside from helping with digestive symptoms, probiotics may also support daily immunity and energy metabolism.
Hydrate the right way: Hydration is about balanced fluid intake. Hypertonic drinks are packed with carbohydrates and calories. They are more suitable after intense physical exercise. Isotonic drinks have a fluid concentration that matches the body’s natural composition. Drinking them during exercise longer than 60 minutes may help with maintaining glycogen levels for athletes.
Time your meals:The type of food and supplements you take before, during, and after exercise should be customized based on your exercise plan. Similarly, the diet you take on the competition day should be optimized for that purpose. Don’t introduce new food or drink on the competition day.
Choose formulations designed for your needs: When you choose sports nutrition supplements, read the ingredients. Understand if the formulation is designed for you. A supplement designed for a 40-year-old endurance athlete has a different nutritional profile than one designed for active women. If you are a competing athlete who gets tested, you want to avoid unintentional intake of banned substances. In that case, check for NSF Certified for Sport and Informed Sport certification.